1. Field of the Invention
This invention relates to a suspension system for a vehicle, and, in particular, to an active suspension system.
2. Description of the Related Art
A conventional active suspension is disclosed in, for example, Japanese Patent Publication 62-96113, laid open to the public on May 2, 1987, a European Patent Application laid open to the public on Aug. 1, 1984 under publications number 0114757, and U.S. Pat. No. 4,371,182, issued on Feb. 1, 1983. In the active suspension as disclosed in the publication enumerated above, a cylinder device is provided for each vehicle wheel member between a vehicle body member and a vehicle wheel member. By controlling a supply of the hydraulic fluid for the cylinder device, the hydraulic fluid in the cylinder device can be changed so that the vehicle suspension characteristics are changed.
In the active suspension system, a hydraulic pressure is detected and a warping of the vehicle body is computed based on the hydraulic pressure detected. A warp control is accomplished by controlling a hydraulic fluid supply for the cylinder device.
The warp control is made based on a hydraulic pressure ratio in the cylinder devices between a right and left front wheels and a hydraulic pressure ratio between a right and left rear wheels. Therefore, if the hydraulic pressure ratio for the front wheels takes the same value as that for the rear wheels, the warp control is not carried out. However, it is desirable to make the warp control, in the case where a lateral acceleration is increased, even when the hydraulic pressure ratios are the same and there is no warping of the vehicle body to so as to obtain an understeer property of the vehicle.